Blood, Sweat, and Fears: A Common Phobia’s Odd Pathophysiology

April 9, 2013 at 1:40 pm
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By John Sanford, Managing Editor for the department of Communications & Public Affairs at the Stanford School of Medicine

I awoke close to midnight. It was the middle of August, in 1992, and the windows were open in the room of the Paris hostel where I was staying. The air was warm and still. My chest felt moist with – sweat? I touched the substance with an index finger and pressed it to my thumb. It felt tacky. Blood!

I put on shorts and flip-flops and walked down a flight of stairs to the men’s bathroom. There, I stood in front of a mirror and contemplated the thin, crimson paste that covered my chest. I ran a hand through it like finger paint, searching for the source. Had I scratched a mole? I was starting to feel nauseated. I opened a faucet and splashed water on my neck, shoulders and torso. I patted myself dry with a paper towel, which soon was covered in damp, pink blotches. Pale and sweating, I turned toward the door, grasped the handle and twisted it. Stepping into the hallway, I collapsed.

A specific phobia is an anxiety disorder in which the presence or anticipation of an object, animal or situation provokes intense and irrational fear. Approximately 12.5 percent of American adults will suffer from at least one such phobia at some period in their lives, according to the National Institute of Mental Health. Where I work, one of my colleagues suffers from a phobia of spiders. (She underwent therapy for the condition several years ago, which helped.) Another colleague has a phobia of riding in elevators and, whenever possible, will take the stairs. Yet another is phobic about driving over bridges.

A phobic reaction starts in the brain but instantly affects other parts of your physiology: Heart rate and blood pressure increase as the sympathetic nervous system activates the body’s fight-or-flight response. Some people may sweat, tremble and feel their muscles tense and heart palpitate.

But blood phobia and its next of kin, injury phobia and injection phobia, are different. (The Diagnostic and Statistical Manual of Mental Disorders groups these phobias together as blood-injection-injury phobia, or BII.) Observing blood seep from a wound, flow into a syringe or spatter on the ground, blood phobics initially will respond like other phobics – that is, their heart rate and blood pressure will increase. But then something else will happen: Their heart rate and blood pressure will suddenly drop, causing dizziness, sweatiness, tunnel vision, nausea, fainting or some combination of these symptoms. This is a vasovagal response. The vagus nerve, a component of the parasympathetic nervous system, meanders from the brain stem through the neck, chest and abdomen. It helps to control involuntary “rest and digest” functions, such as lowering heart rate and promoting the secretion of gastric juices. But when it overreacts – in response to hunger, dehydration, standing up quickly, standing too long, intense laughter, sudden fright, severe coughing, pain, vomiting and, of course blood, among other triggers – it causes a vasovagal response, which does not generally occur with other phobias.

Blood-injury-injection phobia is a fairly common psychiatric disorder: Studies estimate 3 to 4 percent of the population suffers from it. But why would the sight of blood, or for that matter the sight of being stuck by a hypodermic needle, trigger a physiological response that is so different – practically diametric – to that of other phobias? This is the mystery.

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